1. Field of the Invention
The present invention relates to a mobile communication terminal capable of being connected to a plurality of kinds of base stations that use different communication modes.
2. Description of the Related Art
In general, a mobile communication system includes a plurality of base stations which are distributed over the service area. A mobile communication terminal selects one of the base stations, which has the best condition for communication and acquires the selected base station. Thereby, radio communication is enabled.
In the mobile communication system, there may be a case where a part of the standards of the communication mode is upgraded while the system is being in operation. For example, in mobile communication systems using CDMA (Code Division Multiple Access), a preparation is now progressing to upgrade IS95A/IS95B standards to IS2000-1X standards designed to increase a data communication speed, while basic portions of the IS95A/IS95B standards remain unchanged.
It is not possible, however, to upgrade the standards of the communication mode for all the base stations of the system at the same time. In general, the standards are upgraded step by step. Consequently, base stations with different standards are mixedly present in the service area until completion of the work for upgrading the standards for all base stations.
If a mobile communication terminal corresponding to both old and new standards is to start information communication in this state, it is uncertain whether the terminal is connected to a base station with new standards or a base station with old standards, depending on the conditions for communication, such as the current location of the terminal or the condition of radio waves. For example, if the mobile communication terminal of a use who wishes high-speed data communication is connected to a base station with old standards, a longer time than expected may be consumed until completion of data communication, or a high communication charge may occur. This is very disadvantageous.